Abstract：
Acetylation is an important approach to improve the bioactivity of polysaccharides; however, the mechanisms have not been fully understood. As a key component of longan for exerting health promoting function, longan polysaccharide was hypothesized may achieve elevated immunoregulatory activity after acetylation. A bioactive longan polysaccharide (LP) composed of (1 → 6)-α-d-glucan (84.1 %) and with an average Mw of 9.68 × 104 kDa was acetylated to different degree of substitutions (DS) in this study. Key structural changes responsible for improvement in immunoregulatory activity were identified, and underlying mechanisms were investigated. Acetylated LP (Ac-LP) with DS 0.37, 0.78 and 0.92 were obtained. Structural characterization identified the substitution of acetyl groups occurs at O-6 positions of t-Glc non-selectively, while the backbone structure was not apparently changed. This resulted in increased expression of cytokines (IL-10, IL-6 and TNF-α) and ROS production in RAW264.7 macrophages, indicating improved immune activity which is positively related to the DS of Ac-LP. This is attribute to additional cellular receptors for Ac-LP (CD14 and Dectin-1) apart from receptors for LP (TLR4 and Ca2+ receptors), as well as the relative higher protein expression of TLR4-MyD88 signaling pathways. These results would provide guidance for the utilization of acetylated polysaccharides with improved immunoactivity.
摘要：
乙酰化是提高多糖生物活性的重要途径;然而,机制尚未完全理解。龙眼作为发挥促进健康功能的关键成分，据推测，龙眼多糖乙酰化后可能会提高免疫调节活性。在这项研究中，将由（1→6）-α-d-葡聚糖（84.1％）组成的生物活性龙眼多糖（LP）乙酰化为不同程度的取代（DS）。确定了负责改善免疫调节活性的关键结构变化，并对潜在机制进行了研究。获得具有DS0.37、0.78和0.92的乙酰化LP(Ac-LP)。结构表征鉴定乙酰基的取代发生在t-Glc的O-6位非选择性，而骨架结构没有明显改变。这导致RAW264.7巨噬细胞中细胞因子（IL-10，IL-6和TNF-α）和ROS产生的表达增加，表明与Ac-LP的DS呈正相关的免疫活性提高。这归因于Ac-LP的其他细胞受体（CD14和Dectin-1），除了LP的受体（TLR4和Ca2+受体），以及TLR4-MyD88信号通路的蛋白表达相对较高。这些结果将为利用具有改善的免疫活性的乙酰化多糖提供指导。
